Polymer and method for using the polymer for solubilizing nanotubes

ABSTRACT

A new, non-wrapping approach to solubilize nanotubes, such as carbon nanotubes, in organic and inorganic solvents is provided. In accordance with certain embodiments, carbon nanotube surfaces are functionalized in a non-wrapping fashion by functional conjugated polymers that include functional groups for solubilizing such nanotubes. Various embodiments provide polymers that noncovalently bond with carbon nanotubes in a non-wrapping fashion. For example, various embodiments of polymers are provided that comprise a relatively rigid backbone that is suitable for noncovalently bonding with a carbon nanotube substantially along the nanotube&#39;s length, as opposed to about its diameter. In preferred polymers, the major interaction between the polymer backbone and the nanotube surface is parallel π-stacking. The polymers further comprise at least one functional extension from the backbone that are any of various desired functional groups that are suitable for solubilizing a carbon nanotube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/895,161, filed Jul. 20, 2004, which is a continuation of U.S. patentapplication Ser. No. 10/255,122, filed Sep. 24, 2002, which applicationclaimed priority to Provisional Patent Application Ser. No. 60/377,856,filed May 2, 2002 and Provisional Patent Application Ser. No. 60/377,920filed May 2, 2002, the entire disclosures of which are herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention is related to solubilization of nanotubes, andmore particularly to a polymer that is capable of solubilizingnanotubes.

BACKGROUND OF THE INVENTION

A carbon nanotube can be visualized as a sheet of hexagonal graph paperrolled up into a seamless tube and joined. Each line on the graph paperrepresents a carbon-carbon bond, and each intersection point representsa carbon atom.

In general, carbon nanotubes are elongated tubular bodies which aretypically only a few atoms in circumference. The carbon nanotubes arehollow and have a linear fullerene structure. The length of the carbonnanotubes potentially may be millions of times greater than theirmolecular-sized diameter. Both single-walled carbon nanotubes (SWNTs),as well as multi-walled carbon nanotubes (MWNTs) have been recognized.

Carbon nanotubes are currently being proposed for a number ofapplications since they possess a very desirable and unique combinationof physical properties relating to, for example, strength and weight.Carbon nanotubes have also demonstrated electrical conductivity. SeeYakobson, B. I., et al., American Scientist, 85, (1997), 324-337; andDresselhaus, M. S., et al., Science of Fullerenes and Carbon Nanotubes,1996, San Diego: Academic Press, pp. 902-905. For example, carbonnanotubes conduct heat and electricity better than copper or gold andhave 100 times the tensile strength of steel, with only a sixth of theweight of steel. Carbon nanotubes may be produced having extraordinarilysmall size. For example, carbon nanotubes are being produced that areapproximately the size of a DNA double helix (or approximately1/50,000^(th) the width of a human hair).

Considering the excellent properties of carbon nanotubes, they are wellsuited for a variety of uses, from the building of computer circuits tothe reinforcement of composite materials, and even to the delivery ofmedicine. As a result of their properties, carbon nanotubes may beuseful in microelectronic device applications, for example, which oftendemand high thermal conductivity, small dimensions, and light weight.One potential application of carbon nanotubes that has been recognizedis their use in flat-panel displays that use electron field-emissiontechnology (as carbon nanotubes can be good conductors and electronemitters). Further potential applications that have been recognizedinclude electromagnetic shielding, such as for cellular telephones andlaptop computers, radar absorption for stealth aircraft,nano-electronics (including memories in new generations of computers),and use as high-strength, lightweight composites. Further, carbonnanotubes are potential candidates in the areas of electrochemicalenergy storage systems (e.g., lithium ion batteries) and gas storagesystems.

Various techniques for producing carbon nanotubes have been developed.As examples, methods of forming carbon nanotubes are described in U.S.Pat. Nos. 5,753,088 and 5,482,601, the disclosures of which are herebyincorporated herein by reference. The three most common techniques forproducing carbon nanotubes are: 1) laser vaporization technique, 2)electric arc technique, and 3) gas phase technique (e.g., HiPco™process), which are discussed further below.

In general, the “laser vaporization” technique utilizes a pulsed laserto vaporize graphite in producing the carbon nanotubes. The laservaporization technique is further described by A. G. Rinzler et al. inAppl. Phys. A, 1998, 67, 29, the disclosure of which is herebyincorporated herein by reference. Generally, the laser vaporizationtechnique produces carbon nanotubes that have a diameter ofapproximately 1.1 to 1.3 nanometers (nm). Such laser vaporizationtechnique is generally a very low yield process, which requires arelatively long period of time to produce small quantities of carbonnanotubes. For instance, one hour of laser vaporization processingtypically results in approximately 100 milligrams of carbon nanotubes.

Another technique for producing carbon nanotubes is the “electric arc”technique in which carbon nanotubes are synthesized utilizing anelectric arc discharge. As an example, single-walled nanotubes (SWNTs)may be synthesized by an electric arc discharge under helium atmospherewith the graphite anode filled with a mixture of metallic catalysts andgraphite powder (Ni:Y;C), as described more fully by C. Journet et al.in Nature (London), 388 (1997), 756. Typically, such SWNTs are producedas close-packed bundles (or “ropes”) with such bundles having diametersranging from 5 to 20 nm. Generally, the SWNTs are well-aligned in atwo-dimensional periodic triangular lattice bonded by van der Waalsinteractions. The electric arc technique of producing carbon nanotubesis further described by C. Journet and P. Bernier in Appl. Phys. A, 67,1, the disclosure of which is hereby incorporated herein by reference.Utilizing such an electric arc technique, the average carbon nanotubediameter is typically approximately 1.3 to 1.5 nm and the triangularlattice parameter is approximately 1.7 nm. As with the laservaporization technique, the electric arc production technique isgenerally a very low yield process that requires a relatively longperiod of time to produce small quantities of carbon nanotubes. Forinstance, one hour of electric arc processing typically results inapproximately 100 milligrams of carbon nanotubes.

More recently, Richard Smalley and his colleagues at Rice Universityhave discovered another process, the “gas phase” technique, whichproduces much greater quantities of carbon nanotubes than the laservaporization and electric arc production techniques. The gas phasetechnique, which is referred to as the HiPco™ process, produces carbonnanotubes utilizing a gas phase catalytic reaction. The HiPco processuses basic industrial gas (carbon monoxide), under temperature andpressure conditions common in modern industrial plants to createrelatively high quantities of high-purity carbon nanotubes that areessentially free of by-products. The HiPco process is described infurther detail by P. Nikolaev et al. in Chem. Phys. Lett., 1999, 313,91, the disclosure of which is hereby incorporated herein by reference.

While daily quantities of carbon nanotubes produced using theabove-described laser vaporization and electric arc techniques areapproximately 1 gram per day, the HiPco process may enable dailyproduction of carbon nanotubes in quantities of a pound or more.Generally, the HiPco technique produces carbon nanotubes that haverelatively much smaller diameters than are typically produced in thelaser vaporization or electric arc techniques. For instance, thenanotubes produced by the HiPco technique generally have diameters ofapproximately 0.7 to 0.8 nm.

Full-length (unshortened) carbon nanotubes, due to their high aspectratio, small diameter, light weight, high strength, high electrical- andthermal-conductivity, are recognized as the ultimate carbon fibers fornanostructured materials. See Calvert, P. Nature 1999, 399, 210, andAndrews, R. et al. Appl. Phys. Lett. 199, 75, 1329, the disclosures ofwhich are hereby incorporated herein by reference. The carbon nanotubematerials, however, are insoluble in common organic solvents. SeeEbbesen, T. W. Ace. Chem. Res. 1998, 31, 558-556, the disclosure ofwhich is hereby incorporated herein by reference.

Covalent side-wall functionalizations of carbon nanotubes can lead tothe dissolution of carbon nanotubes in organic solvents. It should benoted that the terms “dissolution” and “solubilization” are usedinterchangeably herein. See Boul, P. J. et al., Chem Phys. Lett. 1999,310, 367 and Georgakilas, V. et al., J. Am. Chem. Soc. 2002, 124,760-761, the disclosures of which are hereby incorporated herein byreference. The disadvantage of this approach is that a carbon nanotube'sintrinsic properties are changed significantly by covalent side-wallfunctionalizations.

Carbon nanotubes can also be solubilized in organic solvents and waterby polymer wrapping. See Dalton, A. B. et al., J. Phys. Chem. B 2000,104, 10012-10016, Star, A. et al. Angew. Chem., Int. Ed. 2001, 40,1721-1725, and O'Connell, M. J. et al. Chem. Phys. Lett. 2001, 342,265-271, the disclosures of which are hereby incorporated herein byreference. FIGS. 1A-1C show examples of such polymer wrapping of acarbon nanotube. In polymer wrapping, a polymer “wraps” around thediameter of a carbon nanotube. For instance, FIG. 1 shows an example ofpolymers 102A and 102B wrapping around single-walled carbon nanotube(SWNT) 101. FIG. 1B shows an example of polymer 103A and 103B wrappingaround SWNT 101. FIG. 1C shows an example of polymers 104A and 104Bwrapping around SWNT 101. It should be noted that the polymers in eachof the examples of FIGS. 1A-1C are the same, and the FIGURES illustratethat the type of polymer-wrapping that occurs is random (e.g., the samepolymers wrap about the carbon nanotube in different ways in each ofFIGS. 1A-1C). One disadvantage of this approach is that the polymer isvery inefficient in wrapping the small-diameter single-walled carbonnanotubes produced by the HiPco process because of high strainconformation required for the polymer. For example, such polymerwrapping approach can only solubilize the SWNTs_(HiPco) (i.e., SWNTsproduced by the HiPco process) at about 0.1 mg/ml in organic solvents.SWNT_(HiPco) is the only SWNT material that can be currently produced ata large scale with high purity.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a method for solubilizingnanotubes, a polymer for solubilizing nanotubes, and resultingcompositions of matter that may be formed using solubilized nanotubes.Embodiments of the present invention provide a new approach tosolubilizing nanotubes, such as carbon nanotubes, in solvents. Thesolvents can be, in principle, any solvents. Solubilization of carbonnanotubes in accordance with embodiments of the present invention havebeen experimentally demonstrated in organic solvents and in water. Inaccordance with certain embodiments of the present invention, carbonnanotube surfaces are functionalized in a non-wrapping fashion byfunctional conjugated polymers that include functional groups forsolubilizing such nanotubes. As used herein, “non-wrapping” means notenveloping the diameter of a nanotube. Thus, associating a polymer witha nanotube in a “non-wrapping fashion” encompasses any association ofthe polymer with the nanotube in which the polymer does not completelyenvelop the diameter of the nanotube. When describing certainembodiments of the present invention, the non-wrapping fashion may befurther defined and/or restricted. For instance, in a preferredembodiment of the present invention, a polymer can associate with ananotube (e.g., via π-stacking interaction therewith) wherein thepolymer's backbone extends substantially along the length of thenanotube without any portion of the backbone extending over more thanhalf of the nanotube's diameter in relation to any other portion of thepolymer's backbone.

Various embodiments provide polymers that associate with carbonnanotubes in a non-wrapping fashion. More specifically, variousembodiments of polymers are provided that comprise a relatively rigidbackbone that is suitable for associating with a carbon nanotubesubstantially along the nanotube's length, as opposed to about itsdiameter. In preferred polymers, the major interaction between thepolymer backbone and the nanotube surface is parallel π-stacking. Suchinteraction may result in the polymer non-covalently bonding (orotherwise associating) with the nanotube. Examples of rigid functionalconjugated polymers that may be utilized in embodiments of the presentinvention include, without limitation, poly(aryleneethynylene)s andpoly(3-decylthiophene). In accordance with embodiments of the presentinvention, the polymers further comprise at least one functionalextension from the backbone, wherein such at least one functionextension comprises any of various desired functional groups that aresuitable for solubilizing a carbon nanotube.

In one embodiment of the present invention, a method of solubilizing ananotube is disclosed. The method comprises mixing a polymer with ananotube, and the polymer noncovalently bonding with the nanotube in anon-wrapping fashion, wherein the polymer comprises at least onefunctional portion for solubilizing the nanotube. As used herein,“mixing” is intended to encompass “adding,” “combining,” and similarterms for presenting at least one polymer to at least one nanotube.

In another embodiment of the present invention, a polymer forsolubilizing nanotubes is disclosed. The polymer comprises a backboneportion for noncovalently bonding with a nanotube in a non-wrappingfashion, and at least one functional portion for solubilizing thenanotube.

In another embodiment, a process is disclosed that comprises mixing atleast one polymer with at least one nanotube in a solvent. In certainembodiments, the solvent may comprise an organic solvent, and in otherembodiments the solvent may comprise an aqueous solvent. The mixingresults in the at least one polymer forming a noncovalent bond with theat least one nanotube in a non-wrapping fashion, and the at least onepolymer solubilizing the at least one nanotube.

In another embodiment, a method of solubilizing carbon nanotubes isprovided. The method comprises mixing at least one polymer with at leastone carbon nanotube in a solvent. Again, in certain embodiments, thesolvent may comprise an organic solvent, and in other embodiments thesolvent may comprise an aqueous solvent. The method further comprisesthe at least one polymer interacting with the at least one carbonnanotube's surface via π-stacking, and the at least one polymersolubilizing the at least one carbon nanotube.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawing, in which:

FIGS. 1A-1C show examples of polymer wrapping of carbon nanotubes of theprior art;

FIGS. 2A-2B show an example molecular model of a polymer that associateswith a carbon nanotube in a non-wrapping fashion in accordance with anembodiment of the present invention;

FIGS. 3A-3C show example polymer structures of embodiments of thepresent invention;

FIG. 4 shows another example of a polymer structure that may beimplemented for associating with a carbon nanotube in a non-wrappingfashion in accordance with an embodiment of the present invention;

FIG. 5A shows a graph illustrating the thin film visible and nearinfrared (IR) spectra of SWNTs_(HiPco) (without a polymer associatedtherewith);

FIG. 5B shows a graph illustrating the thin film visible and near IRspectra of SWNTs_(HiPco) solubilized by an example polymer of anembodiment of the present invention;

FIG. 6A shows a transmission electron microscopy (“TEM”) image ofSWNTs_(laser) (i.e., SWNTs produced by the laser technique) solubilizedby an example polymer of an embodiment of the present invention;

FIG. 6B shows a TEM image of SWNTs_(arc) (i.e., SWNTs produced by thearc technique) solubilized by an example polymer of an embodiment of thepresent invention;

FIGS. 6C and 6D show TEM images of SWNTs_(HiPco) solubilized with anexample polymer of an embodiment of the present invention;

FIGS. 7A and 7B show high resolution TEM images of SWNTs_(laser)solubilized with an example polymer of an embodiment of the presentinvention;

FIGS. 8A-8C show high resolution TEM images of SWNTs_(arc) solubilizedwith an example polymer of an embodiment of the present invention; and

FIG. 9 shows a field-emission scanning electron microscopy (“SEM”) image(1.00 kV) of a torn edge of Bucky paper formed in accordance with asolubilization technique of an embodiment of the present invention,which illustrates that the majority of the sample is SWNT nanoribbon.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention are now described withreference to the above figures. Embodiments of the present inventionprovide a new approach to solubilizing nanotubes in solvents.Advantageously, certain embodiments of the present invention may enablesolubilization in organic solvents, and certain embodiments may enablesolubilization in aqueous solvents. This approach is based on adiscovery that carbon nanotube surfaces can be functionalized in anon-wrapping fashion by functional conjugated polymers. For instance, anexample molecular model of a polymer that associates (e.g.,noncovalently bonds) with a carbon nanotube in a non-wrapping fashion isshown in FIGS. 2A-2B. FIG. 2B is a cross-sectional view of FIG. 2A takenas indicated in FIG. 2A. As shown in this example, a carbon nanotube(and more specifically a single-walled carbon nanotube in this example)201 has polymer 202 associated with it in a non-wrapping fashiontherewith.

Polymer 202 comprises a relatively rigid backbone 203 that associateswith carbon nanotube 201 substantially along the length, as opposed toabout the diameter, of such carbon nanotube 201. Thus, polymer 202associates with carbon nanotube 201 in a non-wrapping fashion, which isadvantageous for various reasons, some of which are described more fullyherein. In this example, backbone 203 associates with nanotube 201(e.g., via π-stacking interaction therewith) wherein such backbone 203extends substantially along the length of nanotube 201 without anyportion of backbone 203 extending over more than half of the diameter ofnanotube 201 in relation to any other portion of backbone 203. Forinstance, backbone 203 is sufficiently rigid such that no portionthereof bends to the extent that such portion passes the half-diameter(or “equator line”) 205 of nanotube 201 relative to location 206 ofnanotube 201 at which at least a portion of backbone 203 is associatedwith nanotube 201. The specific rigidity of various backbones 203 thatmay be implemented in accordance with embodiments of the presentinvention may vary (e.g., certain implementations may enable a portionof backbone 203 to bend beyond half-diameter 205 while another portionof such backbone is arranged at location 206 of nanotube 201), but suchbackbones 203 are preferably sufficiently rigid such that they do notwrap (i.e., fully envelop the diameter of) nanotube 201. Of course, asshown in the example of FIGS. 2A-2B, portions of polymer 202 (e.g.,functional extensions 204A and 204B) may extend about all or a portionof the diameter of nanotube 201, but backbone 203 of polymer 202 ispreferably sufficiently rigid such that it does not wrap about thediameter of nanotube 201.

Polymer 202 further comprises various functional extensions frombackbone 203, such as functional extensions 204A and 204B, which maycomprise any of various desired functional groups for functionalizingcarbon nanotube 201. As described further herein, embodiments of thepresent invention include functional groups in polymer 202 that aresuitable for solubilizing carbon nanotube 201.

One advantage of polymer 202 associating with carbon nanotube 201 (e.g.,via π-stacking interaction) in a non-wrapping fashion is that it enablesfunctional groups, such as functional extensions 204A and 204B, to bearranged along backbone 203 in a desired manner to accurately controlthe spacing of such functional groups. In polymers that associate with acarbon nanotube in a wrapping fashion, it becomes much more difficult tocontrol the relative spacing of the functional groups arranged on thepolymer because their spacing is dependent on the wrapping of thepolymer. By controlling the spacing of such functional groups alongbackbone 202, more control may be provided over if/how the functionalgroups interact with each other, carbon nanotube 201, and/or otherelements to which the functional groups may be exposed.

Another advantage of such noncovalent functionalization of carbonnanotubes is that it allows for a significant degree offunctionalization to be added to carbon nanotube surfaces (sidewalls)while still preserving nearly all of the nanotubes' intrinsicproperties. That is, as described above, carbon nanotubes possess a verydesirable and unique combination of physical properties relating to, forexample, strength, weight, electrical conductivity, etc. Having theability to solubilize carbon nanotubes while preserving nearly all ofthe nanotubes' properties thus offers many possibilities in, forexample, material science. For instance, in certain applications, carbonnanotubes may be solubilized and thus used in forming a desiredcomposition of matter (or “material”) that has desired propertiessupplied at least in part by the nanotubes, some examples of which aredescribed further below.

An example of a technique for solubilizing carbon nanotubes wasperformed using rigid functional conjugated polymers,poly(aryleneethynylene)s (also referred to as “1,” “3”, “4” herein). SeeBunz, U. H. F. Chem. Rev. 2000, 100, 1605-1644 and McQuade, D. T et al.,J. Am. Chem. Soc. 2000, 122, 12389-12390, the disclosures of which arehereby incorporated herein by reference, and poly(3-decylthiophene)(also referred to as “2” herein). FIGS. 3A-3C show example polymerstructures of embodiments of the present invention. More specifically,FIG. 3A shows an example poly(aryleneethynylene) (labeled “1”) polymerstructure that may be used to noncovalently bond with a carbon nanotubein a non-wrapping fashion. The example polymer structure shown in FIG.3A comprises functional extensions R₁, R₂, R₃, and R₄, which may, inalternative example implementations for solubilizing carbon nanotubes,be implemented as either 1a, 1b, 1c, or 1d shown hereafter:

R₁=R₄=H, R₂=R₃=OC₁₀H₂₁  (1a)

R₁=R₂=R₃=R₄=F  (1b)

FIG. 3B shows another example poly(aryleneethynylene) (labeled “3” andreferred to herein as “3”) polymer structure that may be used tononcovalently bond with a carbon nanotube in a non-wrapping fashion.Further, FIG. 3C shows another example poly(aryleneethynylene) (labeled“4” and referred to herein as “4”) polymer structure that may be used tononcovalently bond with a carbon nanotube in a non-wrapping fashion.While the example polymer structures 1, 3, and 4 shown in FIGS. 3A-3Care poly(phenyleneethynylene) structures, it should be understood thatother poly(aryleneethynylene)-type structures may be used in accordancewith embodiments of the present invention.

The example polymer structures of FIGS. 3A-3C may be implemented fornoncovalently bonding with a carbon nanotube in a non-wrapping fashion,as with the example shown in FIGS. 2A-2B, for solubilizing such carbonnanotube. Indeed, the example molecular model of FIGS. 2A-2B illustratesan example of implementation 1a, described above, of the polymer of FIG.3A, and more specifically it shows an example of implementation1a_(n=1.5) ⁻ SWNT_((6,6)) complex (i.e., armchair SWNT), wherein n isthe repeat number. It should be understood that the present invention isnot intended to be limited solely to the functional groups of 1a, 1b,1c, and 1d (or the functional groups of polymer structures 3 and 4)shown above for solubilizing carbon nanotubes, but rather any suchfunctional group now known or later developed for solubilizing carbonnanotubes may be used in accordance with embodiments of the presentinvention. Preferably, the solubilizing functional group(s) included inthe polymer do not substantially alter the intrinsic properties of thecarbon nanotube.

FIG. 4 shows another example of a polymer structure that may beimplemented for noncovalently bonding with a carbon nanotube in anon-wrapping fashion. More specifically, FIG. 4 shows an examplestructure of a highly regioregular head-to-tail poly(3-decylthiophene)(labeled “2”) that may be implemented in certain embodiments of thepresent invention.

In contrast to previous work, See Dalton, Star, and O'Connell, M. J. etal., the backbone of 1, 2, 3, and 4 described above is rigid and cannotwrap around the SWNTs, and the major interaction between the polymerbackbone and the nanotube surface is parallel π-stacking. Further, theexample backbones 5-18 described below are also rigid such that they donot wrap around the nanotube, and the major interaction between suchpolymer backbones and the nanotube surface is parallel π-stacking.Parallel π-stacking is one type of noncovalent bonding. See Chen, R. J.et al., J. Am. Chem. Soc., 2001, 123, 3838-3839, the disclosure of whichis hereby incorporated herein by reference. The techniques disclosedherein utilize such polymers to enable the dissolution (or“solubilization”) of various types of carbon nanotubes in organicsolvents (such as CHCl₃, chlorobenzene etc), which represents the firstexample of solubilization of carbon nanotubes via π-stacking withoutpolymer wrapping.

As an example, SWNTs can be readily solubilized in CHCl₃ by mixing with1 (e.g., 1a, 1b, 1c, or 1d), 2, 3, or 4 after vigorous shaking and/orbath-sonication. The minimum weight ratio (WR_(initial)) of1:SWNTs_(HiPco), 2: SWNTs_(HiPco), 3: SWNTs_(HiPco), and 4:SWNTs_(HiPco), required to solubilize the SWNTs_(HiPco)(i.e., SWNTsproduced by the HiPco technique) is about 0.4; and the maximumconcentration of SWNTs_(HiPco)in CHCl₃ is about 5 mg/ml for 1d, whichrepresents the highest solubility of SWNTs_(HiPco)in organic solvents bynoncovalent functionalization. As examples, 13.6 mg of SWNTs_(HiPco)canbe dissolved in 6.8 ml of CHCl₃ in the presence of 5.4 mg of 1a; and20.4 mg of SWNTs_(HiPco)can be dissolved in 4.0 ml of CHCl₃ in thepresence of 20.4 mg of 1d. The maximum concentration of SWNTs_(laser)(i.e., SWNTs produced by the laser technique) and SWNTs_(arc) (i.e.,SWNTs produced by the arc technique) is about 0.5 mg/ml for 1a. Thesolubility of SWNTs can be further improved by optimizing the polymerside chain's length and composition. For example, the longer side chainsand/or the side chains with branched structures can further improve thesolubility of the SWNTs.

As another example, SWNTs can be readily solubilized in deionized waterby mixing with 4 after bath-sonication. For example, 13.7 mg ofSWNTs_(HiPco) can be dissolved in 6.9 ml of deionized water in thepresence of 13.7 mg of 4.

The new polymers (1a-1, n_(average)=19.5; 1a-2, n_(average)=13; 1b,n_(average)=19; 1c, n_(average)=19; 1d) were synthesized andcharacterized according to known methods. See Bunz, U. H. F. Chem. Rev.2000, 100, 1605-1644, the disclosure of which is hereby incorporatedherein by reference. Three types of SWNTs were used in this study: 1)purified HiPco-SWNTs (“SWNTs_(HiPco)”, from Carbon Nanotechnologies,Inc.); 2) purified laser-grown SWNTs (“SWNTs_(laser)”); and 3) purifiedelectric arc-grown SWNTs (“SWNTs_(arc)”). As an example preparationprocedure for 1a-SWNTs_(HiPco) complex: 14.7 mg of SWNTs_(HiPco) wassonicated in 29.4 ml of CHCl₃ for 30 minutes (“min”) to give an unstablesuspension of visible insoluble solids. 14.7 mg of 1a was then added andmost of the visible insoluble solids became soluble simply by vigorousshaking. The resulting solution was further sonicated for 10-30 min togive a black-colored stable solution with no detectable solidprecipitation for over 10 days. Such resulting black-colored andunsaturated carbon nanotube solution was visually nonscattering and noprecipitation occurred upon prolonged standing (e.g., over 10 days). Theproduct was collected by PTFE membrane filtration (0.2-0.8 μm poresize), washed with CHCl₃, and dried at room temperature under vacuum togive 20.6 mg of free-standing black solid film (bucky paper).

The procedures followed in my study for 2-SWNTs_(HiPco),1c-SWNTs_(HiPco), 1b-SWNTs_(HiPco), 1d-SWNTs_(HiPco), 3-SWNTs_(HiPco),1a-SWNTs_(laser) and 1a-SWNTs_(arc) are similar to that described abovefor 1a-SWNTs_(HiPco). The as-prepared SWNTs_(HiPco) and CVD-grownmulti-walled carbon nanotubes (MWNTs) can also be solubilized in CHCl₃by a similar procedure. The as-prepared SWNTs_(arc), however, form anunstable suspension using a similar procedure, presumably due to theamorphous carbon coating on nanotubes that prevents the efficient π-πinteraction between 1 and the nanotube surfaces.

The PTFE membrane filtration and CHCl₃ washing steps were used to removefree 1a. According to the weight gain, the weight ratio (WR_(final)) of1a: SWNTs_(HiPco), in the final product is estimated to be about0.38-0.40, which is independent of WR_(initial). For example, the WRdata in three 1a:SWNTs_(HiPco) reactions are as follows: 1)WR_(initial)=1.00, WR_(final)=0.40; 2) WR_(initial)=0.40,WR_(final)=0.38; 3) WR_(initial)=0.40, WR_(final)=0.39. Although thisestimate is still rough, it strongly suggests that 1 could form stableand irreversibly bound complexes with carbon nanotubes in CHCl₃, insteadof a simple mixture.

A preferred embodiment of the present invention provides a polymer forsolubilizing carbon nanotubes while preserving nearly all of thenanotubes' intrinsic properties. For instance, FIG. 5A shows a graphillustrating the thin film visible and near infrared (IR) spectra ofSWNTs_(HiPco) (without a polymer associated therewith). FIG. 5B shows agraph illustrating the thin film visible and near IR spectra of1a-SWNTs_(HiPco). According to the thin film visible and near-IRspectroscopies, the band structures of 1a-SWNTs_(HiPco) (of FIG. 5B) arevery similar to those of pristine SWNTs_(HiPco), (of FIG. 5A),indicating that the electronic structures of SWNTs_(HiPco), arebasically intact upon polymer complexation. The charge-transfer in1a-SWNTs_(HiPco) is believed to be insignificant based on bothabsorption and Raman spectra. It should be noted that in the spectrum of1a-SWNTs_(HiPco) (of FIG. 5B) there is a very broad signal that isoverlapped with those of SWNTs_(HiPco) (of FIG. 5A) between 3.5 and 2eV, which presumably arises from the lowest energy absorption of 1a inthe nanotube complex.

TABLE 1 Mechanical properties of Bucky paper alone and 1-SWNTsHiPcoBucky paper. SWNTs_(HiPco) 1-SWNTs_(HiPco) Properties Bucky paper Buckypaper (%) Increase Tensile Strength (MPa) 9.74 28.3 190.5 Young'sModulus (GPa) 0.26 4.5 1630.7

For example, bucky paper made of 1-SWNTs_(HiPco), complex (Tensilestrength=29.3 MPa; Young's modulus=4.5 GPa) demonstrates a significantimprovement in mechanical properties compared to those of bucky papermade of pure SWNTs_(HiPco) (Tensile strength=9.74 MPa; Young'smodulus=0.26 GPa), see Table 1. Both types of bucky papers were producedby the same room temperature membrane filtration process (without anyhigh temperature annealing) for better comparison. This shows thatfunctionalized, solubilized nanotubes can increase the adhesion betweennanotubes via more efficient π-π interactions. Accordingly, theresulting bucky paper dissolves more slowly in CHCl₃ at a lowerconcentration (approximately 0.1-0.2 mg/ml of 1a-SWNTs_(HiPco) inCHCl₃). For applications that require high nanotube concentration (forexample, polymer composites), using 1-SWNTs (W=0.4) solution in CHCl₃prepared in situ without filtration is recommended.

Various other soluble functional polymers with π-conjugated backbonestructures may also be used to solubilize carbon nanotubes in organicsolvents in accordance with alternative embodiments of the presentinvention. Some of such polymer backbone structures are shown as below(R represents any organic functional group; Ar represents anyπ-conjugated structure), as structures 5-18:

In the above backbones 5-18, n is preferably greater than or equal to 2,and R represents any organic functional group, such as R=OC₁₀H₂₁,R=C₁₀H₂₁, or other functional group described herein for solubilizingnanotubes, as examples. It should be recognized that the examplebackbones 5-15 are poly (aryleneethynylene)s, backbone 16 is apolyphenylene, backbone 17 is a polypyrrole, and backbone 18 is apolythiophene.

The 1-SWNTs_(HiPco) solution of a preferred embodiment can mixhomogeneously with other polymer solutions such as polycarbonate andpolystyrene. Homogeneous nanotube-polycarbonate and -polystyrenecomposites can be prepared by removing the organic solvents.

As an example, 0.6 ml of a chloroform solution (125 mg/ml) ofpoly(bisphenol A carbonate) was homogeneously mixed with 2.89 ml of achloroform solution (1.3 mg/ml of SWNTs_(HiPco)) of 1a-SWNTs_(HiPco). Ahomogeneous SWNTs/poly(bisphenol A carbonate) composite (5 wt % ofSWNTs_(HiPco)) was formed after removing the chloroform solvent. Byvarying the ratio of 1a-SWNTs_(HiPco):poly(bisphenol A carbonate), aseries of SWNTs/poly(bisphenol A carbonate) composites with differentSWNTs fillings can be easily made.

TABLE 2 Mechanical properties of polycarbonate (PC)/1a-SWNTs_(HiPco)nanocomposite. PC/1a- Properties PC SWNTs_(HiPco) (%) Increase TensileStrength (MPa) 26.0 43.7 68 Break Strain (%) 1.23 19.1 1453

As shown above in Table 2, soluble 1a-SWNTs_(HiPco) complexsignificantly improves the mechanical properties of commercial polymers.For example, the tensile strength and break strain of purepoly(bisphenol A carbonate) are 26 MPa and 1.23%, respectively; 3.8 wt %of SWNTs_(HiPco), filling results in 68% and 1453% increases in tensilestrength (43.7 MPa) and break strain (19.1%) of poly(bisphenol Acarbonate) (average M_(w) approximately 64,000), respectively.

FIGS. 6A-6D, 7A-7B, and 8A-8C show transmission electron microscopy(TEM) images, and FIG. 9 shows a field emission scanning electronmicroscopy (SEM) image, which are described further hereafter. Morespecifically, FIG. 6A shows a TEM image of 1-SWNTs_(laser), FIG. 6Bshows a TEM image of 1-SWNTs_(arc), and FIGS. 6C and 6D show TEM imagesof 1-SWNTs_(HiPco). For reference, the scale bar shown in FIGS. 6A-6D is100 nm.

FIGS. 7A and 7B show high resolution TEM images of 1a-SWNTs_(laser) (120kV, one drop of the freshly prepared chlorobenzene solution of1a-SWNTs_(laser) (approximately 0.05 mg/ml) was placed on a Holey Carbon400 mesh TEM grid (SPI Supplies, Formvar coating was removed) in contactwith a Kimwipes wiper. The solvent was quickly soaked away by the wiper,preventing the aggregation of nanotubes). For reference, the scale barshown in FIGS. 7A-7B is 5 nm.

FIGS. 8A-8C show high resolution TEM images of 1a-SWNTs_(arc) (120 kV,one drop of the freshly prepared chlorobenzene solution of1a-SWNTs_(arc) (approximately 0.05 mg/ml) was placed on a Holey Carbon400 mesh TEM grid (SPI Supplies, Formvar coating was removed) in contactwith a Kimwipes wiper. The solvent was quickly soaked away by the wiper,preventing the aggregation of nanotubes). For reference, the scale barshown in FIGS. 8A-8C is 5 nm.

FIG. 9 shows field-emission SEM image (1.00 kV) of a torn edge of Buckypaper (1a-SWNTs_(HiPco)), illustrating that the majority of sample isSWNT nanoribbon. The TEM images show that the majority of SWNTs in1a-SWNTs_(laser) and 1a-SWNTs_(arc) are small ropes (2-6 nm, see FIGS.6A, 6B, 7A, 7B, and 8A-8C), whereas the majority of SWNTs in1a-SWNTs_(HiPco) are nanoribbon assemblies of small ropes (see FIGS. 6C,6D, and 9). The observation of a twisted SWNT nanoribbon on TEM gridsurface shown in FIG. 6D is indicative of the robustness of such twodimensional (2D) assemblies and further supports a π-stackinginteraction with the polymer backbone oriented along the nanotube'slength. Such nanoribbon is indicative of robustness because if the 2Dassembly is not robust, it will easily collapse into small ropes on theTEM grid surface. It should be possible to prevent such 2D assembly andobtain small ropes and/or individual SWNTs_(HiPco) by using 1, forexample, with bulky and/or ionic functional groups in the end of theside chains.

The bucky paper made of 1-SWNTs_(HiPco), complex (Tensile strength=28.3MPa; Young's modulus=4.5 GPa) demonstrates quantitatively a significantimprovement in mechanical properties compared to those of bucky paper ofpure SWNTs_(HiPco) (Tensile strength=9.74 MPa; Young's modulus=0.26GPa). Both types of bucky papers were produced by the same roomtemperature membrane filtration process (without any high temperatureannealing) for better comparison.

In view of the above, it should be recognized that embodiments of thepresent invention provide a molecular structure that is capable ofnoncovalently bonding with a nanotube (e.g., carbon nanotube) in anon-wrapping manner, and the molecular structure may comprise one ormore functional groups for solubilizing the nanotube to which themolecular structure associates. Preferably, the molecular structureforms a non-covalent bond with the nanotube; however, in certainimplementations the molecular structure may be such that it forms acovalent bond with the nanotube in a non-wrapping fashion.

Solubilization of nanotubes allows for their use in enhancing theproperties of various compositions of matter, including, as one example,plastics. Insoluble nanotubes cannot be dispersed homogeneously incommercial plastics and adhesives; therefore the polymer composites madeby the addition of insoluble nanotubes gave little improvement inmechanical performance of plastics (Ajayan, P. M. et al., Adv. Mater.2000, 12, 750; Schadler, L. S. et al. Appl. Phys. Lett. 1998, 73, 3842).In contrast, soluble nanotubes can significantly improve the mechanicalperformance of plastics, for example. For example, the tensile strengthand break strain of pure poly(bisphenol A carbonate) are 26 MPa and1.23%, respectively; 3.8 wt % of SWNTs_(HiPco), filling results in 68%and 1453% increases in tensile strength (43.7 MPa) and break strain(19.1%) of poly(bisphenol A carbonate) (average M_(w) approximately64,000), respectively.

While various examples above are described for solubilizing carbonnanotubes, and more particularly single-walled carbon nanotubes,embodiments of the present invention are not intended to be limitedsolely in application to carbon nanotubes. Nanotubes may be formed fromvarious materials such as, for example, carbon, boron nitride, andcomposites thereof. The nanotubes may be single-walled nanotubes ormulti-walled nanotubes. Thus, while examples are described herein abovefor solubilizing carbon nanotubes, certain embodiments of the presentinvention may be utilized for solubilizing various other types ofnanotubes, including without limitation multi-walled carbon nanotubes(MWNTs), boron nitride nanotubes, and composites thereof. Accordingly,as used herein, the term “nanotubes” is not limited solely to carbonnanotubes. Rather, the term “nanotubes” is used broadly herein and,unless otherwise qualified, is intended to encompass any type ofnanotube now known or later developed.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

1. A composite comprising: a fibrous material; and functionalized,solubilized nanotubes mixed within the fibrous material, wherein thefunctionalized, solubilized nanotubes comprise a backbone polymerstructure bonded to the nanotubes in a nonwrapping fashion, the backbonecomprising a portion selected from the group consisting of:

wherein M is selected from the group consisting of Ni, Pd, and Pt,

wherein each of R₁-R₈ in the above-listed backbone portions a)-q)represents a functional group; and wherein the composite has an improvedmechanical property compared to that of the fibrous material alone. 2.The composite of claim 1 wherein the fibrous material comprises buckypaper.
 3. The composite of claim 1 wherein the backbone comprises apoly(aryleneethynylene).
 4. The composite of claim 3 wherein thepoly(aryleneethynylene) comprises at least 4 of said functional portions(R₁, R₂, R₃, and R₄), wherein said functional portions comprisefunctional portions selected from the group consisting of: a) R₁=R₄=Hand R₂=R₃=OC₁₀H₂₁, b) R₁=R₂=R₃=R₄=F, c) R₁=R₄=H and R₂=R₃=

d) R₁=R₄=H and R₂=R₃=


5. The composite of claim 1 wherein the backbone comprises apoly(phenyleneethynylene).
 6. The composite of claim 1 wherein thebackbone comprises a poly(3-decylthiophene).
 7. The composite of claim 1wherein the nanotube is a carbon nanotube.
 8. The composite of claim 1wherein the nanotube comprises a single-walled carbon nanotube, amulti-walled carbon nanotube, or a combination thereof.
 9. The compositeof claim 1 further comprising polycarbonate.
 10. The composite of claim1 further comprising polystyrene.
 11. The composite of claim 1 whereinthe at least one functional portion comprises at least one selected fromthe group consisting of: H, OC₁₀H₂₁, F,


12. An article of manufacture comprising the composite of claim 1.